The present invention pertains to a process for manufacturing thermoplastic polymer shaped articles reinforced with long continuous fibers by pultrusion. Prior to the shaping of rovings impregnated with thermoplastic resin, the process comprises compressing the said rovings so as to form a sheet in which the elementary fibers of the rovings are impregnated with thermoplastic resin in the molten state. The sheet is formed by passing the rovings, after impregnation with thermoplastic resin, into a heated rectangular flat die to compress them, thus forcing the molten resin to penetrate between the fibers. The process is applicable to thermoplastic polymers in general, but also makes it possible to obtain a new article made of polyvinyl chloride reinforced with long continuous fibers.
In a general manner, the process of manufacturing thermoplastic resin profiles by pultrusion is known. The usual process consists of impregnating the rovings with resin, then passing the bulk substance into a heated tunnel, for example, using hot air or infrared radiation, at a temperature sufficient to melt the polymer. At the tunnel exit, the rovings coated with resin enter a heated device which gives the final shape to the product being produced, which is cooled as it emerges from the device. This process has one serious disadvantage: the difficulty of melting and homogeneously distributing the thermoplastic resin within the rovings.
A roving is formed from the combination of several continuous elementary fibers. In the pultrusion process, several rovings are impregnated and then pass into the heated tunnel where they combine in bulk with one another to form large-volume bundles or groups of fibers. Radiation heating has difficulty in producing melting of the thermoplastic resin at the core of the bundle and its impregnation of the elementary fibers. This lack of impregnation homogeneity and consequently the entrapment of air between the unimpregnated fibers can be the source of defects in the mechanical properties of the final product. These effects become more significant, the greater the number of rovings and the larger the final shape.
In addition, such a process does not make it possible to produce a rigid polyvinyl chloride shaped article reinforced with long continuous fibers, because of the properties of polyvinyl chloride. Under the conditions of the process, gelling of the polyvinyl chloride, especially in the case where it is free of plasticizer, is impossible to produce by simply raising the temperature without the danger of thermal degradation. At present, gelling is performed in kneading devices which create shearing of the material, essential to gelling. Under the condition of the known processing, the highly incomplete gelling of the matrix results in defective coating of the reinforcement fibers, leading to mediocre-quality shapes or even to fiber breakage when the shape is being drawn.